1. Field of the Invention
The invention is related to the field of bipolar transistors and in particular to a bipolar indium phosphide transistor having a boron phosphide wide gap emitter.
2. Prior Art
Group III-V compound semiconductor transistors are known in the art. Although the solid state industry has been concentrating on the development of gallium arsenide transistors, indium phosphide and boron phosphide transistors separately have been given some attention. Williams et al in U.S. Pat. No. 3,054,936 discloses boron phosphide p-n junction transistors. However, transistors made with boron phosphide alone have low channel mobility and are not suitable for high frequency (microwave) applications. Additionally Katsuto et al in U.S. Pat. No. 4,214,926 disclose doping techniques for boron phosphide films grown on silicon substrates and Japanese Pat. Nos. 1009-582 and 2072-182 describe boron phosphide-silicon heterojunction transistors. Flatley et al in U.S. Pat. No. 3,321,682 disclose diffusion processing techniques for gallium phosphide and indium phosphide while Frank, Crowley and Berenz in their article "Device Development for mm-Waves" Microwave Journal, June 1979, describe the advantages of indium phosphide devices for millimeter wave applications. This article deals mainly with two terminal devices and Gunn Oscillators for millimeter (mm) wave applications.
The theory of wide gap emitters is presented by Kroemer in his article "Theory of a Wide Gap Emitter for Transistors" Proceedings of the IRE, November 1957. Kroemer discloses that the "injection defecit" can be reduced by several orders of magnitude if the emitter has a higher band gap than the base region. Kroemer in a second article "Heterostructure Bipolar Transistors and Integrated Circuits," Proceedings of the IEEE, Vol. 70 No. 1 January 1982 and Dumke, Woodall and Rideout in their article "GaAs-GaAlAs Heterojunction Transistor for High Frequency Operations" Solid State Electronics Vol. 15 1972 disclose the use of wide gap emitters for high frequency application. Both articles are primarily directed to gallium arsenide technology but Kroemer indicates the principle may be applicable to lattice matched III/V compound semiconductor heterosystems.
The invention is a novel indium phosphide-boron phosphide heterojunction bipolar transistor with a wide gap emitter.